Stable carbon isotope ratios in tree rings of co-occurring species from semi arid tropics in Africa: patterns and climatic signals uri icon

abstract

  • Although several proxies have been proposed to trace the course of environmental and climatological fluctuations, precise paleoclimate records from the tropics, notably from Africa are still sorely lacking today. Stable carbon isotopes (d13C) in tree rings are an attractive record of climate. In this study, the patterns and climatic signals of d13C ratios were determined on tree rings of deciduous (Acacia senegal, Acacia tortilis, Acacia seyal) and an evergreen (Balanites aegyptiaca) species, from a semi-arid Acacia Woodland in Ethiopia. d13C inter-annual patterns are synchronous among the co-occurring species. A declining trend with time was observed in d13C, notably for B. aegyptiaca, which could be due to anthropogenic increases in atmospheric CO2 concentration and decrease in atmospheric d13C. Tree ring d13C values of all the species revealed significant negative correlation with precipitation amount but not with temperature and relative humidity. The d13C series of the deciduous species shows a higher correlation (r = - 0.70 to - 0.78) with precipitation than the evergreen species (r = - 0.55). A master d13C series, composed of the average of the three Acacia species, displayed stronger significant correlation (r = - 0.82) than any of the individual species d13C series. The weak relationship between temperature and d13C in this study indicates that photosynthetic rate is not a significant factor. Moisture stress, however, may have a direct impact on the stomatal conductance and explain the strong negative relationship between d13C and precipitation. The results demonstrate the potential of d13C in tree rings to reflect physiological responses to environmental changes as a vehicle for paleoclimatic reconstruction, which is important to understand tree response to past and future climate change

publication date

  • 2009